How to from PCB Reverse Engineer to ORCAD Schematic

The “PCB reverse engineer ” that we’ve been through has to start with the chip. Such as simple low-end electronic watches, music chips, clocks and electronic chips. It has a complete industrial chain from “pulling single crystal, product design, verification, chip manufacturing, chip testing, packaging, chip sales”. In addition to forward design, these previous ones can also reverse these ics. In the past, because the gate size of the chip was small and the number of metal layers was small, it was possible to do the reverse. Now the chip integration is too high and the reverse method with many layers is not feasible (except for some device level chips). Even if you opt for PCB cloning service, it can be difficult.

The following diagram illustrates the process of how to reverse an inverter from an IC object:

① is the real chip to be “reversed”, ② is the real part of the inverter chip partially enlarged, ③ is the layout of the corresponding IC layout, ④ is the connection of the MOS tube traced by ②, and ⑤ is the representation of the inverter used in engineering.

If the scale is too large, too many metal layers of the chip, this kind of “reverse” method by tracing the transistor one by one is not feasible (other aspects of the design idea can be referenced by the section), write logic forward design is correct.

The method of “PCB reverse engineering” schematic diagram from PCB to be discussed below is a bit similar to the above.

1.2 Schematic diagram from “PCB reverse engineering”

The normal design relationship between PCB and schematic diagram is: the schematic diagram is first imported by the schematic netlist. Create a PCB file, through the first party netlist import. Many PCB design tools provide the function of reverse marking between PCB and schematic diagram to correspond to various modifications.

Special Needs:

Now the situation is a little different: you have a PCB file in your hand. It is required to ensure that the component serial number and connection relationship on the PCB cannot be changed. And create a corresponding schematic diagram, how to draw the schematic diagram quickly at this time?

So far I have not found any EDA software that can provide such a function of reverse generating schematic diagrams from PCB files. The specific layout and wiring of the project is shown in the following figure. PCB is not complex and there are many similar modules.

For this kind of PCB reverse engineering “schematic diagram” method is mainly divided into the following steps:

Step1: Create schematic symbols according to PCB components;

Step2: According to the connection between the components in PCB, connect the corresponding Symbol pins in ORCAD;

Step3: Modify the original component label corresponding to the schematic diagram one by one according to the label on the PCB component (for hundreds of thousands of discrete components (such as capacitors, etc.) to modify one by one.

Step4: Import the newly created schematic netlist to see whether the PCB connection and the number of components have changed for final confirmation.

[Step1] excel can be used to easily build ORCAD symbols for large complex devices on PCB such as BGA devices.

[Step2] The most traditional method is to draw the line by line according to the connection of each pin of each component. For example, when the PCB connection is very complex, unless the object is very valuable or the task requires it, not many people are willing to do this kind of complex work. Since this project has a small number of connections and many buses and modules, the most traditional approach is sufficient.

For very complex schematics, you can refer to the following idea. The network name of the PCB network connection is used in the schematic SYMBOL generated in the first step. And in ORCAD connection between components of the line. All you need to do is write a script to automatically add the network name contained in the PIN to a piece of wire pulled from the ORCAD SYMBOL (the same network name for the wires in ORCAD means they are connected). For such components, it is very efficient to automatically assign network names to the wires after pulling out the wires in a row).

[Step3] Modify the Reference of the component on the schematic diagram and the corresponding label on the PCB. For larger IC chips, a smaller number of time can be tolerated. And hundreds of discrete components such as capacitors to the PCB and the schematic sequence number one by one to correspond. Inevitably, the process of going back and forth between the two pieces of software is quite time-consuming and laborious.

[Step4] After schematic diagram “PCB reverse engineering”. It can be imported into PCB through netlist, and see whether the number of components and connection relationship of PCB have changed to confirm whether there is an error in the process. If it is necessary to “modify and optimize” the product on this basis, the traditional method is used to modify and reverse the standard.